Weeks after the 9/11 terrorist attacks, the Bush administration declared the military exempt from a major plank of the US Constitution's bill of rights, according to a legal memorandum uncovered this week.

The fourth amendment protects Americans from unreasonable searches and seizures. The military exemption, crafted in October 2001 by the justice department lawyers who give legal advice to the president, was cited in a footnote to a 2003 brief on interrogation tactics. That later brief emerged for the first time late Tuesday.

In the 2003 footnote, Bush lawyer John Yoo writes: "Our office recently concluded that the fourth amendment had no application to domestic military operations."

The American Civil Liberties Union (ACLU), which won release of the 2003 brief following a prolonged court battle, argues that the fourth amendment exemption provided legal cover for the administration's programme of eavesdropping on calls without a warrant. That spying was conducted by the US national security agency, a military affiliate.

The White House denied that the October 2001 brief was legally linked to Bush-approved surveillance and said the fourth amendment exemption was later revoked.

"We disagree with the proposition that the fourth amendment has no application to domestic military operations,'' justice department spokesman Brian Roehrkasse told the Associated Press.

"Whether a particular search or seizure is reasonable under the fourth amendment requires consideration of the particular context and circumstances of the search."

Roehrkasse did not provide the date that the administration ended its freedom from the fourth amendment.

Still, the administration had freed itself from part of the US bill of rights for at least 16 months after 9/11. The March 2003 legal brief referred to the fourth amendment exemption as still in place.

The ACLU first noticed the 37-page fourth amendment brief on a list of justice department documents that the Bush administration said were relevant to a lawsuit over government surveillance. The group plans to continue fighting in court for total de-classification of the brief.

"The administration's lawyers believe the president should be permitted to violate statutory law, to violate international treaties, and even to violate the fourth amendment inside the US," Jameel Jaffer, director of the ACLU's national security project, said. "They believe that the president should be above the law."